A buffer solution is 0.100 mol L^-1 in both C₆H₅COOH and C₆H₅COOLi and has a pH of 4.19. Which of the following pH values would you expect after the addition of a small amount of a strong base? A) 3.89 B) 3.69 C) 5.69 D) 4.49 E) 8.89

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Quizplus · Accepted Answer

A buffer solution resists changes in pH upon the addition of small amounts of acid or base. To determine the pH change after the addition of a strong base, we need to consider the components of the buffer solution and how they will react with the added base. The buffer solution contains both C₆H₅COOH (the acid) and C₆H₅COOLi (the salt of the acid). When a strong base is added, it will react with the acid in the buffer solution to form its conjugate base. The salt present in the buffer solution will then react with the added conjugate base to reform the original acid. The overall result is that the concentration of the acid and conjugate base in the buffer solution will remain relatively constant, and the pH of the solution will remain stable. Since the pH of the buffer solution is 4.19, we know that the concentration of H+ ions is 10^-4.19 = 6.49 x 10^-5 M. Because the buffer solution contains equal amounts of the acid and salt, we can assume that the initial concentration of the conjugate base is also 0.100 mol L^-1. When a strong base is added, it will react with the acid in the buffer solution to neutralize some of the H+ ions. This will shift the equilibrium towards the conjugate base, increasing its concentration. The concentration of the acid will decrease, but only slightly since it is present in excess in the buffer solution. The best choice among the answer options is D (4.49), as it is the only one close to the original pH of the buffer solution. The pH of the solution will increase slightly after the addition of the strong base, but it will still be within the acidic range. The exact pH change will depend on the amount of strong base added and the overall buffering capacity of the solution.

A Buffer Solution Is 0